(Not Applicable)
(Not Applicable)
The invention relates to helicopter storage and shipment and, more particularly, to folding of helicopter blades to reduce space required for storage or other purposes.
The large radial dimensions of a helicopter rotor assembly cause a parked helicopter to occupy a space which is large relative to actual body dimensions. For helicopter storage, transport or shipboard use, for example, the space requirements for a helicopter may be reduced by up to two thirds by removal of the main rotor blades.
Removal of the main blades of a helicopter is disadvantageous because of time and equipment requirements, the need for separate blade storage and, perhaps most importantly, requirements for blade balancing, test and recertification which may apply if individual blades are physically separated from their operating positions on the rotor hub assembly.
Alternatively, space requirements may be reduced by folding helicopter blades back to positions overlying or contiguous to the helicopter tail assembly. Many approaches to blade folding have previously been proposed. Approaches relying upon mechanisms added to the rotor hub assembly to enable automated blade folding typically add significant additional complexity, weight and cost to the rotor hub assembly, and may raise reliability issues. Approaches based on temporarily attaching a mechanical assembly between a hub and blade at the time a blade is to folded typically involve complex mechanisms which may be difficult to install, may not permit two-dimensional placement of blade tips, may require modifications to the rotor mechanism, and may have other inherent functional or reliability limitations. For example, some such approaches are subject to the limitation that at least one bolt or pin between each blade and its blade mounting position must remain in its original position during folding, thereby limiting freedom of action during folding.
Helicopter blades, during operation, are rotated principally in a horizontal plane. If a blade is folded by swinging it back with movement only in two dimensions (e.g., in a horizontal plane) the blade tip will be positioned at a significant vertical distance above the tail section. If, during folding, blade movement in a third dimension is also enabled (i.e., blade tip movement vertically), the end of the blade may be brought down closer to the tail section of the helicopter permitting the lowered blade tip to be secured to or near the tail section. This movement of a helicopter blade tip downward from its normal operating alignment during blade folding will be termed xe2x80x9cblade droopxe2x80x9d for present purposes. Prior mechanisms or techniques have not permitted blade droop or have otherwise been subject to limitations or cost or complexity disadvantages.
Objects of the present invention are, therefore, to provide new and improved blade folding units and methods having one or more of the following characteristics and capabilities:
readily installable at time of folding;
low complexity, reliable construction;
installation using existing apertures in blades and blade support components;
blade folding while retaining blade attachment to its hub position;
three-dimensional blade folding with blade droop;
low cost construction; and
ease of technician field use without dependence on special tools or external power sources.
In accordance with the invention, a blade fold hinge unit, usable with a helicopter blade attached to a blade support via two blade pins to enable blade folding with removal of both blade pins while retaining blade connection continuity, includes two portions. The first portion is configured for pivotal attachment to the blade via a first pin positionable in alignable apertures in the first portion and the blade upon removal of one of the blade pins. The second portion is configured for pivotal attachment to the blade support via a second pin positionable in alignable apertures in the second portion and the blade support upon such removal of the blade pin. The hinge unit includes a hinge pin positioned in aligned apertures in the first and second portions to pivotally hinge the first portion to the second portion, the center line of the hinge pin extending transversely to the insertion axes of the first and second pins. The blade fold hinge unit is configured to enable attachment between the blade and blade support upon such removal of one of the two blade pins and to maintain connection continuity of the blade to the blade support via the hinge unit upon removal of the other blade pin for blade folding.
The blade fold hinge unit may also include a pivot limit pin positioned in slots of predetermined length to limit pivotally hinged displacement of the first portion relative to the second portion, to permit drooping of the free end of the blade downward. A lock link may be configured for contact with the second portion to restrain its pivotal displacement relative to the blade support and may also restrict relative motion of the first and second portions subsequent to movement of the blade to a folded position. A restraining strut may be employed to restrain pivotal motion of a folded blade relative to the blade support.
Also in accordance with the invention, a method for folding and drooping a helicopter blade attached to a blade support via two blade pins, with removal of both such blade pins while retaining blade connection continuity, includes the following steps:
(a) removing one blade pin from first apertures in the blade and first apertures in the blade support, so that the blade can then be rotated forward;
(b) attaching a first portion of a hinge unit to the blade via a pin positioned in the first apertures in the blade;
(c) attaching a second portion of the hinge unit to the blade support via a pin positioned in the first apertures in the blade support;
(d) removing the other blade pin from second apertures in the blade and second apertures in the blade support;
(e) pivoting the blade to a folded position; and
(f) pivoting the first portion relative to the second portion to droop the free end of the blade downward.
Further steps may be included to address installing of the lock link and restraining strut referred to above.
For a better understanding of the invention, together with other and further objects, reference is made to the accompanying drawings and the scope of the invention will be pointed out in the accompanying claims.